2 files changed, 193 insertions, 0 deletions
diff --git a/spec/experiments/application_experiment/cache_spec.rb b/spec/experiments/application_experiment/cache_spec.rb
new file mode 100644
index 00000000000..a420d557155
--- /dev/null
+++ b/spec/experiments/application_experiment/cache_spec.rb
@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe ApplicationExperiment::Cache do
+  let(:key_name) { 'experiment_name' }
+  let(:field_name) { 'abc123' }
+  let(:key_field) { [key_name, field_name].join(':') }
+  let(:shared_state) { Gitlab::Redis::SharedState }
+
+  around do |example|
+    shared_state.with { |r| r.del(key_name) }
+    example.run
+    shared_state.with { |r| r.del(key_name) }
+  end
+
+  it "allows reading, writing and deleting", :aggregate_failures do
+    # we test them all together because they are largely interdependent
+
+    expect(subject.read(key_field)).to be_nil
+    expect(shared_state.with { |r| r.hget(key_name, field_name) }).to be_nil
+
+    subject.write(key_field, 'value')
+
+    expect(subject.read(key_field)).to eq('value')
+    expect(shared_state.with { |r| r.hget(key_name, field_name) }).to eq('value')
+
+    subject.delete(key_field)
+
+    expect(subject.read(key_field)).to be_nil
+    expect(shared_state.with { |r| r.hget(key_name, field_name) }).to be_nil
+  end
+
+  it "handles the fetch with a block behavior (which is read/write)" do
+    expect(subject.fetch(key_field) { 'value1' }).to eq('value1') # rubocop:disable Style/RedundantFetchBlock
+    expect(subject.fetch(key_field) { 'value2' }).to eq('value1') # rubocop:disable Style/RedundantFetchBlock
+  end
+
+  it "can clear a whole experiment cache key" do
+    subject.write(key_field, 'value')
+    subject.clear(key: key_field)
+
+    expect(shared_state.with { |r| r.get(key_name) }).to be_nil
+  end
+
+  it "doesn't allow clearing a key from the cache that's not a hash (definitely not an experiment)" do
+    shared_state.with { |r| r.set(key_name, 'value') }
+
+    expect { subject.clear(key: key_name) }.to raise_error(
+      ArgumentError,
+      'invalid call to clear a non-hash cache key'
+    )
+  end
+
+  context "when the :caching_experiments feature is disabled" do
+    before do
+      stub_feature_flags(caching_experiments: false)
+    end
+
+    it "doesn't write to the cache" do
+      subject.write(key_field, 'value')
+
+      expect(subject.read(key_field)).to be_nil
+    end
+  end
+end
diff --git a/spec/experiments/application_experiment_spec.rb b/spec/experiments/application_experiment_spec.rb
new file mode 100644
index 00000000000..ece52d37351
--- /dev/null
+++ b/spec/experiments/application_experiment_spec.rb
@@ -0,0 +1,127 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe ApplicationExperiment do
+  subject { described_class.new(:stub) }
+
+  describe "publishing results" do
+    it "tracks the assignment" do
+      expect(subject).to receive(:track).with(:assignment)
+
+      subject.publish(nil)
+    end
+
+    it "pushes the experiment knowledge into the client using Gon.global" do
+      expect(Gon.global).to receive(:push).with(
+        {
+          experiment: {
+            'stub' => { # string key because it can be namespaced
+              experiment: 'stub',
+              key: 'e8f65fd8d973f9985dc7ea3cf1614ae1',
+              variant: 'control'
+            }
+          }
+        },
+        true
+      )
+
+      subject.publish(nil)
+    end
+  end
+
+  describe "tracking events", :snowplow do
+    it "doesn't track if excluded" do
+      subject.exclude { true }
+
+      subject.track(:action)
+
+      expect_no_snowplow_event
+    end
+
+    it "tracks the event with the expected arguments and merged contexts" do
+      subject.track(:action, property: '_property_', context: [
+        SnowplowTracker::SelfDescribingJson.new('iglu:com.gitlab/fake/jsonschema/0-0-0', { data: '_data_' })
+      ])
+
+      expect_snowplow_event(
+        category: 'stub',
+        action: 'action',
+        property: '_property_',
+        context: [
+          {
+            schema: 'iglu:com.gitlab/fake/jsonschema/0-0-0',
+            data: { data: '_data_' }
+          },
+          {
+            schema: 'iglu:com.gitlab/gitlab_experiment/jsonschema/0-3-0',
+            data: { experiment: 'stub', key: 'e8f65fd8d973f9985dc7ea3cf1614ae1', variant: 'control' }
+          }
+        ]
+      )
+    end
+  end
+
+  describe "variant resolution" do
+    it "returns nil when not rolled out" do
+      stub_feature_flags(stub: false)
+
+      expect(subject.variant.name).to eq('control')
+    end
+
+    context "when rolled out to 100%" do
+      it "returns the first variant name" do
+        subject.try(:variant1) {}
+        subject.try(:variant2) {}
+
+        expect(subject.variant.name).to eq('variant1')
+      end
+    end
+  end
+
+  context "when caching" do
+    let(:cache) { ApplicationExperiment::Cache.new }
+
+    before do
+      cache.clear(key: subject.name)
+
+      subject.use { } # setup the control
+      subject.try { } # setup the candidate
+
+      allow(Gitlab::Experiment::Configuration).to receive(:cache).and_return(cache)
+    end
+
+    it "caches the variant determined by the variant resolver" do
+      expect(subject.variant.name).to eq('candidate') # we should be in the experiment
+
+      subject.run
+
+      expect(cache.read(subject.cache_key)).to eq('candidate')
+    end
+
+    it "doesn't cache a variant if we don't explicitly provide one" do
+      # by not caching "empty" variants, we effectively create a mostly
+      # optimal combination of caching and rollout flexibility. If we cached
+      # every control variant assigned, we'd inflate the cache size and
+      # wouldn't be able to roll out to subjects that we'd already assigned to
+      # the control.
+      stub_feature_flags(stub: false) # simulate being not rolled out
+
+      expect(subject.variant.name).to eq('control') # if we ask, it should be control
+
+      subject.run
+
+      expect(cache.read(subject.cache_key)).to be_nil
+    end
+
+    it "caches a control variant if we assign it specifically" do
+      # by specifically assigning the control variant here, we're guaranteeing
+      # that this context will always get the control variant unless we delete
+      # the field from the cache (or clear the entire experiment cache) -- or
+      # write code that would specify a different variant.
+      subject.run(:control)
+
+      expect(cache.read(subject.cache_key)).to eq('control')
+    end
+  end
+end